1. Field of the Invention
The present invention relates to the field of directional light modulation, 3D displays, emissive micro displays, 2D/3D switchable displays.
2. Prior Art
In 3D displays, directional modulation of the emitted light is necessary to create the 3D viewing perception. In a typical 3D display, a backlight with uniform illumination in multiple illumination directions is required to display images of the same scene from different directions by utilizing some combination of spatial multiplexing and temporal multiplexing in the spatial light modulator. In these 3D displays the light that typically comes from the directional backlight is usually processed by a directionally selective filter (such as diffractive plate or a holographic optical plate for example) before it reaches the spatial light modulator pixels that modulate the light color and intensity while keeping its directionality.
Currently available directional light modulators are a combination of an illumination unit comprising multiple light sources and a directional modulation unit that directs the light emitted from the light sources to a designated direction (see FIGS. 1A, 1B & 1C). As illustrated in FIGS. 1A, 1B & 1C which depict several variants of the prior art, an illumination unit is usually combined with an electro-mechanical movement device such as scanning mirrors or rotating barriers (see U.S. Pat. Nos. 6,151,167, 6,433,907, 6,795,221, 6,803,561, 6,924,476, 6,937,221, 7,061,450, 7,071,594, 7,190,329, 7,193,758, 7,209,271, 7,232,071, 7,482,730, 7,486,255, 7,580,007, 7,724,210 and 7,791,810, and U.S. Patent Application Publication Nos. 2010/0026960 and 2010/0245957, or electro-optically such as liquid lenses or polarization switching (see FIGS. 1A, 1B & 1C and U.S. Pat. Nos. 5,986,811, 6,999,238, 7,106,519, 7,215,475, 7,369,321, 7,619,807 and 7,952,809).
In both electro-mechanically and electro-optically modulated directional light modulators there are three main drawbacks:
1. Response time: The mechanical movement or optical surface change are typically not achieved instantaneously and affect the modulator response time. In addition, the speed of these operations usually takes up some portion of the image frame time that reduces the achievable display brightness.
2. Volumetric aspects: These methods need a distance between the light source and directional modulation device to work with, which increases the total volume of the display.
3. Light loss: Coupling light on to a moving mirror creates light losses which in turn degrades the display system power efficiency and creates heat that has to be eliminated by incorporating bulky cooling methods that add more volume and increased power consumption.
In addition to being slow, bulky and optically lossy, the prior art directional backlight units need to have narrow spectral bandwidth, high collimation and individual controllability for being combined with a directionally selective filter for 3D display purposes. Achieving narrow spectral bandwidth and high collimation requires device level innovations and optical light conditioning, increasing the cost and the volumetric aspects of the overall display system. Achieving individual controllability requires additional circuitry and multiple light sources increasing the system complexity, bulk and cost. U.S. patent application Ser. No. 13/329,107 introduced a novel spatio-optical directional light modulator that overcomes most all of these drawbacks, however its angular coverage is limited by the numerical aperture of its light collimation optics.
It is therefore an objective of this invention to introduce an extended angular coverage spatio-temporal light modulator that overcomes the limitation of the prior art, thus making it feasible to create 3D and high resolution 2D displays that provide the volumetric advantages plus a viewing experience over a wide viewing angle. Additional objectives and advantages of this invention will become apparent from the following detailed description of a preferred embodiment thereof that proceeds with reference to the accompanying drawings.